1. Field of the Invention
The invention relates to an antenna cover for covering an antenna, and it particularly relates to an antenna cover that lessens cyclically wavy distortions of the antenna directivity.
2. Description of Related Art
An antenna cover is often provided to protect an antenna from various external influences and impacts, and the like. Examples of such an antenna cover are described in WO2005/055366, Japanese Patent Application Publication No. 06-140823 (JP-A-6-140823), and Japanese Patent Application Publication No. 2009-278501 (JP-A-2009-278501).
WO2005/055366 describes providing a radio wave absorber at an inner face of a sidewall of a rectangular parallelepiped cover such that the radio wave absorber absorbs the unwanted radio waves propagating horizontally.
JP-A-6-140823 describes a cover that has a flat center portion located above an antenna and an outer peripheral portion that is formed by bending the outer periphery of the center portion. According to this cover, the sensitivities in low elevation angle directions are enhanced with the outer peripheral portion made larger in thickness than the center portion.
JP-A-2009-278501 describes a cover that is structured such that the lower the elevation angle, the larger the thickness of the cover, thus enhancing the sensitivities in low elevation angle directions.